Abstract
Knockdown resistance (kdr) is a mechanism that confers nerve insensitivity to DDT and pyrethroid insecticides. This type of resistance is best characterized in the house fly where several kdr alleles, including the more potent super-kdr factor, have been identified. Resistance is thought to result from a modification of the voltage-sensitive sodium channel, the primary target site for these insecticides, and this is supported by genetic evidence that both kdr and super-kdr map closely to the house fly para-type sodium channel gene. To investigate the molecular basis of resistance, we have sequenced the full 6.3kb coding region of this gene from susceptible, kdr and super-kdr strains. Our results suggest that kdr is caused by a single amino acid substitution, leucine to phenylalanine, in the domain IIS6 segment of the channel; while an additional methionine to threonine change in the nearby IIS4-IIS5 linker is responsible for the enhanced resistance of super-kdr. Using this information, we have developed a PCR-based diagnostic technique for detecting the kdr mutation in individual house flies.
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